Replace NULL with nullptr in all C++ files.

webrtc/voice_engine/channel_manager.cc

Index: webrtc/voice_engine/channel_manager.cc
diff --git a/webrtc/voice_engine/channel_manager.cc b/webrtc/voice_engine/channel_manager.cc
index b8ffe6e796c239734e4748fd1e5d87305bdc527f..757f585c3b8e40da7c9a65d7be14ffbe59401ddd 100644
--- a/webrtc/voice_engine/channel_manager.cc
+++ b/webrtc/voice_engine/channel_manager.cc
@@ -67,7 +67,7 @@ ChannelOwner ChannelManager::GetChannel(int32_t channel_id) {
     if (channels_[i].channel()->ChannelId() == channel_id)
       return channels_[i];
   }
-  return ChannelOwner(NULL);
+  return ChannelOwner(nullptr);
 }
 
 void ChannelManager::GetAllChannels(std::vector<ChannelOwner>* channels) {
@@ -80,7 +80,7 @@ void ChannelManager::DestroyChannel(int32_t channel_id) {
   assert(channel_id >= 0);
   // Holds a reference to a channel, this is used so that we never delete
   // Channels while holding a lock, but rather when the method returns.
-  ChannelOwner reference(NULL);
+  ChannelOwner reference(nullptr);
   {
     rtc::CritScope crit(&lock_);
     std::vector<ChannelOwner>::iterator to_delete = channels_.end();
@@ -125,7 +125,7 @@ ChannelManager::Iterator::Iterator(ChannelManager* channel_manager)
 Channel* ChannelManager::Iterator::GetChannel() {
   if (iterator_pos_ < channels_.size())
     return channels_[iterator_pos_].channel();
-  return NULL;
+  return nullptr;
 }
 
 bool ChannelManager::Iterator::IsValid() {